Notch1 regulates the fate of cardiac progenitor cells

Effect of DNA methylation on the osteogenic differentiation of mesenchymal stem cells: concise review

Mesenchymal stem cells (MSCs) have promising potential for bone tissue engineering in bone healing and regeneration. They are regarded as such due to their capacity for self-renewal, multiple differentiation, and their ability to modulate the immune response. However, changes in the molecular pathways and transcription factors of MSCs in osteogenesis can lead to bone defects and metabolic bone diseases. DNA methylation is an epigenetic process that plays an important role in the osteogenic differentiation of MSCs by regulating gene expression. An increasing number of studies have demonstrated the significance of DNA methyltransferases (DNMTs), Ten-eleven translocation family proteins (TETs), and MSCs signaling pathways about osteogenic differentiation in MSCs. This review focuses on the progress of research in these areas.

Charting the Path: Navigating Embryonic Development to Potentially Safeguard against Congenital Heart Defects

Congenital heart diseases (CHDs) are structural or functional defects present at birth due to improper heart development. Current therapeutic approaches to treating severe CHDs are primarily palliative surgical interventions during the peri- or prenatal stages, when the heart has fully developed from faulty embryogenesis. However, earlier interventions during embryonic development have the potential for better outcomes, as demonstrated by fetal cardiac interventions performed in utero, which have shown improved neonatal and prenatal survival rates, as well as reduced lifelong morbidity. Extensive research on heart development has identified key steps, cellular players, and the intricate network of signaling pathways and transcription factors governing cardiogenesis. Additionally, some reports have indicated that certain adverse genetic and environmental conditions leading to heart malformations and embryonic death may be amendable through the activation of alternative mechanisms. This review first highlights key molecular and cellular processes involved in heart development. Subsequently, it explores the potential for future therapeutic strategies, targeting early embryonic stages, to prevent CHDs, through the delivery of biomolecules or exosomes to compensate for faulty cardiogenic mechanisms. Implementing such non-surgical interventions during early gestation may offer a prophylactic approach toward reducing the occurrence and severity of CHDs.

Deciphering Cardiac Biology and Disease by Single-Cell Transcriptomic Profiling

By detecting minute molecular changes in hundreds to millions of single cells, single-cell RNA sequencing allows for the comprehensive characterization of the diversity and dynamics of cells in the heart. Our understanding of the heart has been transformed through the recognition of cellular heterogeneity, the construction of regulatory networks, the building of lineage trajectories, and the mapping of intercellular crosstalk. In this review, we introduce cardiac progenitors and their transcriptional regulation during embryonic development, highlight cellular heterogeneity and cell subtype functions in cardiac health and disease, and discuss insights gained from the study of pluripotent stem-cell-derived cardiomyocytes.

Peptide-based supramolecular hydrogels for local drug delivery

Peptide-based supramolecular hydrogels have shown great promise as drug delivery systems (DDSs) because of their excellent biocompatibility, biodegradability, biological function, synthetic feasibility, and responsiveness to external stimuli. Self-assembling peptide molecules are able rationally designed into specific nanoarchitectures in response to the different environmental factors under different circumstances. Among all stimuli that have been investigated, utilizing inherent biological microenvironment, such as metal ions, enzymes and endogenous redox species, to trigger self-assembly endows such systems spatiotemporal controllability to transport therapeutics more accurately. Materials formed by weak non-covalent interactions result in the shear-thinning and immediate recovery behavior. Thus, they are injectable via a syringe or catheter, making them the ideal vehicles to deliver drugs. Based on the above merits, self-assembling peptide-based DDSs have been applied to treat various diseases via direct administration at the lesion site. Herein, in this review, we outline the triggers for inducing peptide-based hydrogels formation and serving as DDSs. We also described the advancements of peptide-based supramolecular hydrogels for local drug delivery, including intratumoral, subcutaneous, ischemia-related tissue (intramyocardial, intrarenal, and ischemic hind limb), and ocular administration. Finally, we give a brief perspective about the prospects and challenges in this field.

Molecular characteristics of oocytes and somatic cells of follicles at different sizes that influence in vitro oocyte maturation and embryo production

During the last 10 to 15 yr, in vitro research to predict antral follicle growth and oocyte maturation has delivered interesting advances in the knowledge of processes regulating follicle growth and developmental competence of oocytes. This review discusses the contribution of cumulus and mural granulosa cells in the process of oocyte maturation and cumulus expansion in cumulus-oocyte complexes (COCs) from follicles of different sizes and shows that differences in gene expression in oocytes, granulosa, and theca cells of small and large follicles impact the success of in vitro blastocyst development. In addition, the molecular mechanisms by which COC metabolism and antioxidant defense provide oocyte competence are highlighted. Furthermore, new insights and perspectives on molecular and cellular regulation of in vitro oocyte maturation are emphasized.

RHOQ is induced by DLL4 and regulates angiogenesis by determining the intracellular route of the Notch intracellular domain

Angiogenesis, the formation of new blood vessels by endothelial cells, is a finely tuned process relying on the balance between promoting and repressing signalling pathways. Among these, Notch signalling is critical in ensuring appropriate response of endothelial cells to pro-angiogenic stimuli. However, the downstream targets and pathways effected by Delta-like 4 (DLL4)/Notch signalling and their subsequent contribution to angiogenesis are not fully understood. We found that the Rho GTPase, RHOQ, is induced by DLL4 signalling and that silencing RHOQ results in abnormal sprouting and blood vessel formation both in vitro and in vivo. Loss of RHOQ greatly decreased the level of Notch signalling, conversely overexpression of RHOQ promoted Notch signalling. We describe a new feed-forward mechanism regulating DLL4/Notch signalling, whereby RHOQ is induced by DLL4/Notch and is essential for the NICD nuclear translocation. In the absence of RHOQ, Notch1 becomes targeted for degradation in the autophagy pathway and NICD is sequestered from the nucleus and targeted for degradation in lysosomes.

Dysregulation of Notch signaling in cardiac mesenchymal cells of patients with tetralogy of Fallot

BACKGROUND

Tetralogy of Fallot (TF) is a severe congenital defect of heart development. Fine-tuned sequential activation of Notch signaling genes is responsible for proper heart chamber development. Mutations in Notch genes have been associated with TF. The aim of this study was to analyze the activity of the Notch pathway in cardiac mesenchymal cells derived from ventricular tissue of TF patients.

METHODS

Cardiac mesenchymal cells were isolated from 42 TF patients and from 14 patients with ventricular septal defects (VSDs), used as a comparison group. The Notch pathway was analyzed by estimating the expression of Notch-related genes by qPCR. Differentiation and proliferation capacity of the cells was estimated.

RESULTS

The TF-derived cells demonstrated a dysregulated pattern of Notch-related gene expression comparing to VSD-derived cells. Correlation of Notch signaling activation level by HEY1/HES1 expression level with proliferation and cardiogenic-like differentiation of cardiac mesenchymal cells was observed but not with clinical parameters nor with the age of the patients.

CONCLUSIONS

The data suggest a contribution of dysregulated Notch signaling to the pathogenesis of tetralogy of Fallot and importance of Notch signaling level for the functional state of cardiac mesenchymal cells, which could be critical considering these cells for potential cell therapy approaches.

WD40 repeat and FYVE domain containing 3 is essential for cardiac development

AIMS

WD40 repeat and FYVE domain containing 3 (WDFY3) is an adaptor protein involved in selective degradation of protein aggregates by autophagy. Recent studies have revealed that Wdfy3 is critical in the regulation of brain development and osteoclastogenesis in vivo. However, the function of Wdfy3 in cardiac development remains completely unknown. In this study, we explore the role of Wdfy3 in cardiac morphogenesis using Wdfy3-deficient mice.

METHODS AND RESULTS

Wdfy3 was expressed in the developing heart in mice and peaked at embryonic day 12.5 (E12.5). Loss of Wdfy3 in mice led to embryonic and neonatal lethality. Wdfy3-deficient mice displayed various congenital heart defects including membranous ventricular septal defect (VSD), aortic overriding (AO), double outlet right ventricle (DORV), thinning of ventricular wall, ventricular dilation, and disorganized ventricular trabeculation at E14.5. Cell proliferation was reduced in the hearts from Wdfy3-deficient mice at E12.5 and E14.5, which was associated with enhanced p21 expression. Cardiomyocyte differentiation was diminished as demonstrated by reduced Myh6 and MLC2v in Wdfy3-deficient mice at E14.5. In addition, Nkx2-5 and Mef2c, two cardiac transcription factors regulating cardiomyocyte differentiation, were decreased in Wdfy3-deficient mice at E14.5. Apoptotic cell death remained unaltered. These data suggest that reduced cell proliferation and cardiomyocyte differentiation contribute to cardiac defects in Wdfy3-deficient mice. Mechanistically, loss of Wdfy3 led to a reduction in protein levels of Notch 1 intracellular domain and its downstream targets Hes1 and Hey1, which was accompanied with enhanced full-length Notch1 protein levels. In vitro luciferase assay showed that Wdfy3 deficiency induced activity of p21 promoter, while diminished activity of Hes1 promoter through modulation of Notch1 signalling. Moreover, Wdfy3 was co-localized with Notch1 in primary embryonic cardiomyocytes. Endogenous Wdfy3 physically interacted with full-length Notch1 in the developing heart. These results suggest that Notch1 signalling is perturbed in the hearts from Wdfy3-deficient mice. No alteration of autophagy was detected in the hearts from Wdfy3-deficient mice.

CONCLUSION

Taken together, our data suggest that Wdfy3 plays an essential role in cardiac development, which may be mediated by modulation of Notch1 signalling.

Paeonol Reverses Adriamycin Induced Cardiac Pathological Remodeling through Notch1 Signaling Reactivation in H9c2 Cells and Adult Zebrafish Heart

Adriamycin is a commonly prescribed chemotherapeutic drug for a wide range of cancers. Adriamycin causes cardiotoxicity as an adverse effect that limits its clinical application in cancer treatment. Several mechanisms have been proposed to explain the toxicity it causes in heart cells. Disruption of inherent cardiac repair mechanism is the least understood mechanism of Adriamycin-induced cardiotoxicity. Adriamycin induces pathological remodeling in cardiac cells by promoting apoptosis, hypertrophy, and fibrosis. We found that Adriamycin inhibited Notch1 in a time- and dose-dependent manner in H9c2 cells. We used Paeonol, a Notch1 activator, and analyzed the markers of apoptosis, hypertrophy, and fibrosis in H9c2 cells in vitro and in adult zebrafish heart in vivo as model systems to study Adriamycin-induced cardiotoxicity. Paeonol activated Notch1 signaling and expression of its downstream target genes effectively in the Adriamycin-treated condition in vitro and in vivo. Also we detected that Notch activation using Paeonol protected the cells from apoptosis, collagen deposition, and hypertrophy response using functional assays. We conclude that Adriamycin induced cardiotoxicity by promoting the pathological cardiac remodeling through inhibition of Notch1 signaling and that the Notch1 reactivation by Paeonol protected the cells and reversed the cardiotoxicity.

Aging and stress induced β cell senescence and its implication in diabetes development

Cellular senescence is a well-established defensive mechanism for tumor suppression, and is also proposed to play a crucial role in embryonic development, wound repair, aging and age-related diseases. Senescent cell is characterized by the marked morphological changes and active metabolism along with a distinctive senescence associated secretion phenotype (SASP). Cellular senescence is triggered by multiple endogenous and exogenous stressors, which collectively induce three types of senescence. It is believed that senescence represents a programmed phenomenon to facilitate β cell functional maturation and, therefore, senescence has been suggested to be involved in β cell regeneration, insulin secretion and diabetes development. Nevertheless, despite past extensive studies, the exact impact of senescence on β cell viability, regeneration and functionality, and its relevance to the development of diabetes are yet to be fully addressed. In this review, we will summarize the recent progress in β cell senescence, through which we intend to spark more instructive discussion and perspective with regard to the mechanisms underlying β cell senescence and their links to the pathogenesis of diabetes and the development of therapeutic strategies.

Stem Cell Therapy for Hypoplastic Left Heart Syndrome: Mechanism, Clinical Application, and Future Directions

Hypoplastic left heart syndrome is a type of congenital heart disease characterized by underdevelopment of the left ventricle, outflow tract, and aorta. The condition is fatal if aggressive palliative operations are not undertaken, but even after the complete 3-staged surgical palliation, there is significant morbidity because of progressive and ultimately intractable right ventricular failure. For this reason, there is interest in developing novel therapies for the management of right ventricular dysfunction in patients with hypoplastic left heart syndrome. Stem cell therapy may represent one such innovative approach. The field has identified numerous stem cell populations from different tissues (cardiac or bone marrow or umbilical cord blood), different age groups (adult versus neonate-derived), and different donors (autologous versus allogeneic), with preclinical and clinical experience demonstrating the potential utility of each cell type. Preclinical trials in small and large animal models have elucidated several mechanisms by which stem cells affect the injured myocardium. Our current understanding of stem cell activity is undergoing a shift from a paradigm based on cellular engraftment and differentiation to one recognizing a primarily paracrine effect. Recent studies have comprehensively evaluated the individual components of the stem cells' secretomes, shedding new light on the intracellular and extracellular pathways at the center of their therapeutic effects. This research has laid the groundwork for clinical application, and there are now several trials of stem cell therapies in pediatric populations that will provide important insights into the value of this therapeutic strategy in the management of hypoplastic left heart syndrome and other forms of congenital heart disease. This article reviews the many stem cell types applied to congenital heart disease, their preclinical investigation and the mechanisms by which they might affect right ventricular dysfunction in patients with hypoplastic left heart syndrome, and finally, the completed and ongoing clinical trials of stem cell therapy in patients with congenital heart disease.

Peptide-Based Functional Biomaterials for Soft-Tissue Repair

Synthetically derived peptide-based biomaterials are in many instances capable of mimicking the structure and function of their full-length endogenous counterparts. Combine this with the fact that short mimetic peptides are easier to produce when compared to full length proteins, show enhanced processability and ease of modification, and have the ability to be prepared under well-defined and controlled conditions; it becomes obvious why there has been a recent push to develop regenerative biomaterials from these molecules. There is increasing evidence that the incorporation of peptides within regenerative scaffolds can result in the generation of structural recognition motifs that can enhance cell attachment or induce cell signaling pathways, improving cell infiltration or promote a variety of other modulatory biochemical responses. By highlighting the current approaches in the design and application of short mimetic peptides, we hope to demonstrate their potential in soft-tissue healing while at the same time drawing attention to the advances made to date and the problems which need to be overcome to advance these materials to the clinic for applications in heart, skin, and cornea repair.

Predicting Functional Responses of Progenitor Cell Exosome Potential with Computational Modeling

Congenital heart disease can lead to severe right ventricular heart failure (RVHF). We have shown that aggregated c‐kit⁺ progenitor cells (CPCs) can improve RVHF repair, likely due to exosome‐mediated effects. Here, we demonstrate that miRNA content from monolayer (2D) and aggregated (3D) CPC exosomes can be related to in vitro angiogenesis and antifibrosis responses using partial least squares regression (PLSR). PLSR reduced the dimensionality of the data set to the top 40 miRNAs with the highest weighted coefficients for the in vitro biological responses. Target pathway analysis of these top 40 miRNAs demonstrated significant fit to cardiac angiogenesis and fibrosis pathways. Although the model was trained on in vitro data, we demonstrate that the model can predict angiogenesis and fibrosis responses to exosome treatment in vivo with a strong correlation with published in vivo responses. These studies demonstrate that PLSR modeling of exosome miRNA content has the potential to inform preclinical trials and predict new promising CPC therapies. stem cells translational medicine2019;8:1212–1221

The Notch pathway: a novel therapeutic target for cardiovascular diseases?

Introduction: The Notch pathway is involved in determining cell fate during development and postnatally in continuously renewing tissues, such as the endothelium, the epithelium, and in the stem cells pool. The dysregulation of the Notch pathway is one of the causes of limited response, or resistance, to available cancer treatments and novel therapeutic strategies based on Notch inhibition are being investigated in preclinical and clinical studies in oncology. A large body of evidence now shows that the dysregulation of the Notch pathway is also involved in the pathophysiology of cardiovascular diseases (CVDs). Areas covered: This review discusses the molecular mechanisms involving Notch which underlie heart failure, aortic valve calcification, and aortic aneurysm. Expert opinion: Despite the existence of preventive, pharmacological and surgical interventions approaches, CVDs are the first causes of mortality worldwide. The Notch pathway is becoming increasingly recognized as being involved in heart failure, aortic aneurysm and aortic valve calcification, which are among the most common global causes of mortality due to CVDs. As already shown in cancer, the dissection of the biological processes and molecular mechanisms involving Notch should pave the way for new strategies to prevent and cure these diseases.

The Best for the Most Important: Maintaining a Pristine Proteome in Stem and Progenitor Cells

Pluripotent stem cells give rise to reproductively enabled offsprings by generating progressively lineage-restricted multipotent stem cells that would differentiate into lineage-committed stem and progenitor cells. These lineage-committed stem and progenitor cells give rise to all adult tissues and organs. Adult stem and progenitor cells are generated as part of the developmental program and play critical roles in tissue and organ maintenance and/or regeneration. The ability of pluripotent stem cells to self-renew, maintain pluripotency, and differentiate into a multicellular organism is highly dependent on sensing and integrating extracellular and extraorganismal cues. Proteins perform and integrate almost all cellular functions including signal transduction, regulation of gene expression, metabolism, and cell division and death. Therefore, maintenance of an appropriate mix of correctly folded proteins, a pristine proteome, is essential for proper stem cell function. The stem cells' proteome must be pristine because unfolded, misfolded, or otherwise damaged proteins would interfere with unlimited self-renewal, maintenance of pluripotency, differentiation into downstream lineages, and consequently with the development of properly functioning tissue and organs. Understanding how various stem cells generate and maintain a pristine proteome is therefore essential for exploiting their potential in regenerative medicine and possibly for the discovery of novel approaches for maintaining, propagating, and differentiating pluripotent, multipotent, and adult stem cells as well as induced pluripotent stem cells. In this review, we will summarize cellular networks used by various stem cells for generation and maintenance of a pristine proteome. We will also explore the coordination of these networks with one another and their integration with the gene regulatory and signaling networks.

SDF-1α promotes repair of myocardial ischemic necrosis zones in rats

OBJECTIVE

To explore the repair effect of stromal cell-derived factor-1α (SDF-1α) on myocardial ischemic necrosis zones.

METHODS

Lentivirus (LV-SDF-1α-GFP) containing SDF-1α target gene was established, the separated and cultured neonatal rat cardiac fibroblasts were transfected, and caudal intravenous injection of isoproterenol was conducted to prepare a rat model of myocardial ischemia. Small animal ultrasound was used to evaluate the effect on cardiac functions. Morphology and immunofluorescence were used to observe the change of ischemic necrosis zones and expressions of stem cellular markers c-kit, CD34, nkx2.5, and nanog, and a quantitative analysis was performed.

RESULTS

The established LV-SDF-1α-GFP was used to transfect myocardial fibroblasts which presented GFP green fluorescent expression and could secrete SDF-1α. The small animal ultrasound system showed that rat cardiac functions of the lentivirus group and cell group were improved to different degrees, myocardial ischemic necrosis zones of lentivirus group and cell group were reduced, and differences had statistical significances (P<0.05). Immunofluorescence showed that expressions of stem cellular markers c-kit, CD34, nkx2.5 and nanog in myocardial tissue ischemic zones in both the lentivirus group and cell group increased, and differences through inter-group comparison had statistical significances (P<0.05).

CONCLUSION

SDF-1α can promote migration and proliferation of stem cells into the myocardial ischemic necrosis zone, participate in repair of the myocardial necrosis zone, and improve cardiac function.

Reversible Notch1 acetylation tunes proliferative signalling in cardiomyocytes

Aims

The Notch signalling pathway regulates the balance between proliferation and differentiation in several tissues, including the heart. Our previous work has demonstrated that the proliferative potential of neonatal cardiomyocytes relies on Notch1 activity. A deep investigation on the biochemical regulation of the Notch signalling in cardiomyocytes is the focus of the current research.

Methods and results

We show that the Notch1 intracellular domain is acetylated in proliferating neonatal rat cardiomyocytes and that acetylation tightly controls the amplitude and duration of Notch signalling. We found that acetylation extends the half-life of the protein, and enhanced its transcriptional activity, therefore counteracting apoptosis and sustaining cardiomyocyte proliferation. Sirt1 acted as a negative modulator of Notch1 signalling; its overexpression in cardiomyocytes reverted Notch acetylation and dampened its stability. A constitutively acetylated fusion protein between Notch1 and the acetyltransferase domain of p300 promoted cardiomyocyte proliferation, which was remarkably sustained over time. Viral vector-mediated expression of this protein enhanced heart regeneration after apical resection in neonatal mice.

Conclusion

These results identify the reversible acetylation of Notch1 as a novel mechanism to modulate its signalling in the heart and tune the proliferative potential of cardiomyocytes.

Three in a Box: Understanding Cardiomyocyte, Fibroblast, and Innate Immune Cell Interactions to Orchestrate Cardiac Repair Processes

Following an insult by both intrinsic and extrinsic pathways, complex cellular, and molecular interactions determine a successful recovery or inadequate repair of damaged tissue. The efficiency of this process is particularly important in the heart, an organ characterized by very limited regenerative and repair capacity in higher adult vertebrates. Cardiac insult is characteristically associated with fibrosis and heart failure, as a result of cardiomyocyte death, myocardial degeneration, and adverse remodeling. Recent evidence implies that resident non-cardiomyocytes, fibroblasts but also macrophages -pillars of the innate immunity- form part of the inflammatory response and decisively affect the repair process following a cardiac insult. Multiple studies in model organisms (mouse, zebrafish) of various developmental stages (adult and neonatal) combined with genetically engineered cell plasticity and differentiation intervention protocols -mainly targeting cardiac fibroblasts or progenitor cells-reveal particular roles of resident and recruited innate immune cells and their secretome in the coordination of cardiac repair. The interplay of innate immune cells with cardiac fibroblasts and cardiomyocytes is emerging as a crucial platform to help our understanding and, importantly, to allow the development of effective interventions sufficient to minimize cardiac damage and dysfunction after injury.

Recovery of the Xenopus laevis heart from ROS-induced stress utilizes conserved pathways of cardiac regeneration

Urodele amphibians and some fish are capable of regenerating up to a quarter of their heart tissue after cardiac injury. While many anuran amphibians like Xenopus laevis are not capable of such feats, they are able to repair lesser levels of cardiac damage, such as that caused by oxidative stress, to a far greater degree than mammals. Using an optogenetic stress induction model that utilizes the protein KillerRed, we have investigated the extent to which mechanisms of cardiac regeneration are conserved during the restoration of normal heart morphology post oxidative stress in X. laevis tadpoles. We focused particularly on the processes of cardiomyocyte proliferation and dedifferentiation, as well as the pathways that facilitate the regulation of these processes. The cardiac response to KillerRed-induced injury in X. laevis tadpole hearts consists of a phase dominated by indicators of cardiac stress, followed by a repair-like phase with characteristics similar to mechanisms of cardiac regeneration in urodeles and fish. In the latter phase, we found markers associated with partial dedifferentiation and cardiomyocyte proliferation in the injured tadpole heart, which, unlike in regenerating hearts, are not dependent on Notch or retinoic acid signaling. Ultimately, the X. laevis cardiac response to KillerRed-induced oxidative stress shares characteristics with both mammalian and urodele/fish repair mechanisms, but is nonetheless a unique form of recovery, occupying an intermediate place on the spectrum of cardiac regenerative ability. An understanding of how Xenopus repairs cardiac damage can help bridge the gap between mammals and urodeles and contribute to new methods of treating heart disease.

Aggregation of Child Cardiac Progenitor Cells Into Spheres Activates Notch Signaling and Improves Treatment of Right Ventricular Heart Failure

RATIONALE

Congenital heart disease can lead to life-threatening right ventricular (RV) heart failure. Results from clinical trials support expanding cardiac progenitor cell (CPC) based therapies. However, our recent data show that CPCs lose function as they age, starting as early as 1 year.

OBJECTIVE

To determine whether the aggregation of child (1-5-year-old) CPCs into scaffold-free spheres can improve differentiation by enhancing Notch signaling, a known regulator of CPC fate. We hypothesized that aggregated (3-dimensional [3D]) CPCs will repair RV heart failure better than monolayer (2-dimensional [2D]) CPCs.

METHODS AND RESULTS

Spheres were produced with 1500 CPCs each using a microwell array. CPC aggregation significantly increased gene expression of Notch1 compared with 2D CPCs, accompanied by significant upregulation of cardiogenic transcription factors (GATA4, HAND1, MEF2C, NKX2.5, and TBX5) and endothelial markers (CD31, FLK1, FLT1, VWF). Blocking Notch receptor activation with the γ-secretase inhibitor DAPT (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) diminished these effects. To evaluate the therapeutic improvements of CPC aggregation, RV heart failure was induced in athymic rats by pulmonary artery banding, and cells were implanted into the RV free wall. Echocardiographic measurements 28 days postimplantation showed significantly improved RV function with 3D compared with 2D CPCs. Tracking implanted CPCs via DiR (1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide)-labeling showed improved retention of 3D CPCs. Transducing 3D CPCs with Notch1-shRNA (short hairpin RNA) did not reduce retention, but significantly reduced RV functional improvements. Histological analyses showed 3D treatment reduced RV fibrosis and increased angiogenesis. Although 3D CPCs formed CD31⁺ vessel-like cells in vivo, these effects are more likely because of improved 3D CPC exosome function compared with 2D CPC exosomes.

CONCLUSIONS

Spherical aggregation improves child CPC function in a Notch-dependent manner. The strong reparative ability of CPC spheres warrants further investigation as a treatment for pediatric heart failure, especially in older children where reparative ability may be reduced.

Notch signal pathway - therapeutic target for regulation of reparative processes in the heart

Notch signaling pathway is a universal regulator of cell fate in embryogenesis and in maintaining the cell homeostasis of adult tissue. Through local cell-cell interactions, he controls neighboring cells behavior and determines their capacity for self-renewal, growth, survival, differentiation, and apoptosis. Recent studies have shown that the control of regenerative processes in the heart is also carried out with the participation of Notch system. At the heart of Notch regulates migration bone marrow progenitors and stimulates the proliferation of cardiomyocytes, cardiac progenitor cell activity, limits cardiomyocyte hypertrophy and fibrosis progression and stimulates angiogenesis. Notch signaling pathway may be regarded as a very promising target for the development of drugs for the stimulation of regeneration in the myocardium.

Hypoxia-stressed cardiomyocytes promote early cardiac differentiation of cardiac stem cells through HIF-1α/Jagged1/Notch1 signaling

Hypoxia is beneficial for the differentiation of stem cells transplanted for myocardial injury, but mechanisms underlying this benefit remain unsolved. Here, we report the impact of hypoxia-induced Jagged1 expression in cardiomyocytes (CMs) for driving the differentiation of cardiac stem cells (CSCs). Forced hypoxia-inducible factor 1α (HIF-1α) expression and physical hypoxia (5% O₂) treatment could induce Jagged1 expression in neonatal rat CMs. Pharmacological inhibition of HIF-1α by YC-1 attenuated hypoxia-promoted Jagged1 expression in CMs. An ERK inhibitor (PD98059), but not inhibitors of JNK (SP600125), Notch (DAPT), NF-κB (PTDC), JAK (AG490), or STAT3 (Stattic) suppressed hypoxia-induced Jagged1 protein expression in CMs. c-Kit⁺ CSCs isolated from neonatal rat hearts using a magnetic-activated cell sorting method expressed GATA4, SM22α or vWF, but not Nkx2.5 and cTnI. Moreover, 87.3% of freshly isolated CSCs displayed Notch1 receptor expression. Direct co-culture of CMs with BrdU-labeled CSCs enhanced CSCs differentiation, as evidenced by an increased number of BrdU⁺/Nkx2.5⁺ cells, while intermittent hypoxia for 21 days promoted co-culture-triggered differentiation of CSCs into CM-like cells. Notably, YC-1 and DAPT attenuated hypoxia-induced differentiation. Our results suggest that hypoxia induces Jagged1 expression in CMs primarily through ERK signaling, and facilitates early cardiac lineage differentiation of CSCs in CM/CSC co-cultures via HIF-1α/Jagged1/Notch signaling.

Notch pathway activation enhances cardiosphere in vitro expansion

Cardiospheres (CSps) are self‐assembling clusters of a heterogeneous population of poorly differentiated cells outgrowing from in vitro cultured cardiac explants. Scanty information is available on the molecular pathways regulating CSp growth and their differentiation potential towards cardiac and vascular lineages. Here we report that Notch1 stimulates a massive increase in both CSp number and size, inducing a peculiar gene expression programme leading to a cardiovascular molecular signature. These effects were further enhanced using Adeno‐Associated Virus (AAV)‐based gene transfer of activated Notch1‐intracellular domain (N1‐ICD) or soluble‐Jagged1 (sJ1) ligand to CSp‐forming cells. A peculiar effect was exploited by selected pro‐proliferating miRNAs: hsa‐miR‐590‐3p induced a cardiovascular gene expression programme, while hsa‐miR‐199a‐3p acted as the most potent stimulus for the activation of the Notch pathway, thus showing that, unlike in adult cardiomyocytes, these miRNAs involve Notch signalling activation in CSps. Our results identify Notch1 as a crucial regulator of CSp growth and differentiation along the vascular lineage, raising the attracting possibility that forced activation of this pathway might be exploited to promote in vitro CSp expansion as a tool for toxicology screening and cell‐free therapeutic strategies.

Heterocellular molecular contacts in the mammalian stem cell niche

Adult tissue homeostasis and repair relies on prompt and appropriate intervention by tissue-specific adult stem cells (SCs). SCs have the ability to self-renew; upon appropriate stimulation, they proliferate and give rise to specialized cells. An array of environmental signals is important for maintenance of the SC pool and SC survival, behavior, and fate. Within this special microenvironment, commonly known as the stem cell niche (SCN), SC behavior and fate are regulated by soluble molecules and direct molecular contacts via adhesion molecules providing connections to local supporting cells and the extracellular matrix. Besides the extensively discussed array of soluble molecules, the expression of adhesion molecules and molecular contacts is another fundamental mechanism regulating niche occupancy and SC mobilization upon activation. Some adhesion molecules are differentially expressed and have tissue-specific consequences, likely reflecting the structural differences in niche composition and design, especially the presence or absence of a stromal counterpart. However, the distribution and identity of intercellular molecular contacts for adhesion and adhesion-mediated signaling within stromal and non-stromal SCN have not been thoroughly studied. This review highlights common details or significant differences in cell-to-cell contacts within representative stromal and non-stromal niches that could unveil new standpoints for stem cell biology and therapy.

Molecular basis of functional myogenic specification of Bona Fide multipotent adult cardiac stem cells

Ischemic Heart Disease (IHD) remains the developed world's number one killer. The improved survival from Acute Myocardial Infarction (AMI) and the progressive aging of western population brought to an increased incidence of chronic Heart Failure (HF), which assumed epidemic proportions nowadays. Except for heart transplantation, all treatments for HF should be considered palliative because none of the current therapies can reverse myocardial degeneration responsible for HF syndrome. To stop the HF epidemic will ultimately require protocols to reduce the progressive cardiomyocyte (CM) loss and to foster their regeneration. It is now generally accepted that mammalian CMs renew throughout life. However, this endogenous regenerative reservoir is insufficient to repair the extensive damage produced by AMI/IHD while the source and degree of CM turnover remains strongly disputed. Independent groups have convincingly shown that the adult myocardium harbors bona-fide tissue specific cardiac stem cells (CSCs). Unfortunately, recent reports have challenged the identity and the endogenous myogenic capacity of the c-kit expressing CSCs. This has hampered progress and unless this conflict is settled, clinical tests of repair/regenerative protocols are unlikely to provide convincing answers about their clinical potential. Here we review recent data that have eventually clarified the specific phenotypic identity of true multipotent CSCs. These cells when coaxed by embryonic cardiac morphogens undergo a precisely orchestrated myogenic commitment process robustly generating bona-fide functional cardiomyocytes. These data should set the path for the revival of further investigation untangling the regenerative biology of adult CSCs to harness their potential for HF prevention and treatment.

MiR34 inhibition induces human heart progenitor proliferation

MiR34 involvement in myocardial injury repair and ageing has been well documented in mouse model. Our aim was to establish whether the inhibition of miR34 expression through locked nucleic acid (LNA) could be used as a pharmacological intervention to enhance human heart repair. Cardiac progenitor cells were obtained by right atrial specimen collection during intraoperative procedures. Our analysis revealed a direct correlation between miR34 expression and patient age, and its silencing by LNA promoted the cardiac progenitor growth rate up to twofold ( ± 0.8). Our results confirmed the relevance of miR34a in human heart ageing, as previously demonstrated in mouse. Moreover, the decrease of miR34 expression in the cardiac progenitor cell population indicates its role in maintaining an undifferentiated status and consequently in a lower proliferation rate with the involvement of genes such as Notch-1, Numb, and p63.

Beyond cardiomyocyte loss: Role of Notch in cardiac aging

The knowledge of the cellular events occurring in the aging heart has dramatically expanded in the last decade and is expected to further grow in years to come. It is now clear that impaired function and loss of cardiomyocytes are major features of cardiac aging, but other events are likewise important. In particular, accumulating experimental evidence highlights the importance of fibroblast and cardiac progenitor cell (CPC) dysfunction. The Notch pathway regulates cardiomyocyte, fibroblast, and CPC activity and, thus, may be critically involved in heart disease associated with advanced age, especially heart failure. In a translational perspective, thorough investigation of the Notch system in the aging myocardium may lead to the identification of molecular targets for novel therapies for age-related cardiac disease.

Notch and Senescence

Cellular senescence, previously thought of as an autonomous tumour suppressor mechanism, is emerging as a phenotype and effector present throughout the life of an organism from embryogenesis to senile decline. Senescent cells have powerful non-autonomous effects upon multiple players within their microenvironment mainly through their secretory phenotype. How senescent cells co-ordinate numerous, sometimes functionally contrasting outputs through their secretome had previously been unclear. The Notch pathway, originally identified for its involvement in Drosophila wing development, has more recently been found to underpin diverse effects in human cancer. Here we discuss recent findings that suggest that Notch is intimately involved in the development of senescence and how it acts to co-ordinate the composition and functional effects of the senescence secretome. We also highlight the complex physical and functional interplay between Notch and p53, critical to both senescence and cancer. Understanding the interplay between Notch, p53 and senescence could allow us develop the therapeutics of the future for cancer and ageing.

Biological outcome and mapping of total factor cascades in response to HIF induction during regenerative angiogenesis

Hypoxia Inducible Factor (HIF) is the main transcription factor that mediates cell response to hypoxia. Howeverthe complex factor cascades induced by HIF during regenerative angiogenesis are currently incompletely mapped and the biological outcome mediated by chronic HIF induction during vessel regeneration are not well known. Here, we investigated the biological impact of HIF induction on vascular regeneration and identified the differentially regulated genes during regeneration, HIF induction and hypoxic regeneration. The use of the fin zebrafish regeneration model revealed that exposure to HIF inducer (cobalt chloride) prevents vessel differentiation by maintaining their vascular plexuses in an immature state. The regenerated fins are easily breakable, lacking completely endochondral ossification. Gene expression arrays combined to gene functional enrichment analysis revealed that regenerative process and HIF induction shared the regulation of common genes mainly involved in DNA replication and proteasome complex. HIF induction during regeneration affected the expression of exclusive genes involved in cell differentiation and communication, consistent with the observed immature vascular plexuses of the regenerated fins during HIF induction. The use of morpholino (MO) knockdown strategy revealed that the expression of some of these genes such as tubulin and col10a1 are required for fin regeneration. Taken together, this study revealed the impact of HIF induction on regenerative angiogenesis and provided a framework to develop a gene network leading to regenerative process during HIF expression.

Pathologic Stimulus Determines Lineage Commitment of Cardiac C-kit+ Cells

BACKGROUND

Although cardiac c-kit⁺ cells are being tested in clinical trials, the circumstances that determine lineage differentiation of c-kit⁺ cells in vivo are unknown. Recent findings suggest that endogenous cardiac c-kit⁺ cells rarely contribute cardiomyocytes to the adult heart. We assessed whether various pathological stimuli differentially affect the eventual cell fates of c-kit⁺ cells.

METHODS

We used single-cell sequencing and genetic lineage tracing of c-kit⁺ cells to determine whether various pathological stimuli would result in different fates of c-kit⁺ cells.

RESULTS

Single-cell sequencing of cardiac CD45^-c-kit⁺ cells showed innate heterogeneity, indicative of the existence of vascular and mesenchymal c-kit⁺ cells in normal hearts. Cardiac pressure overload resulted in a modest increase in c-kit-derived cardiomyocytes, with significant increases in the numbers of endothelial cells and fibroblasts. Doxorubicin-induced acute cardiotoxicity did not increase c-kit-derived endothelial cell fates but instead induced cardiomyocyte differentiation. Mechanistically, doxorubicin-induced DNA damage in c-kit⁺ cells resulted in expression of p53. Inhibition of p53 blocked cardiomyocyte differentiation in response to doxorubicin, whereas stabilization of p53 was sufficient to increase c-kit-derived cardiomyocyte differentiation.

CONCLUSIONS

These results demonstrate that different pathological stimuli induce different cell fates of c-kit⁺ cells in vivo. Although the overall rate of cardiomyocyte formation from c-kit⁺ cells is still below clinically relevant levels, we show that p53 is central to the ability of c-kit⁺ cells to adopt cardiomyocyte fates, which could lead to the development of strategies to preferentially generate cardiomyocytes from c-kit⁺ cells.

Cardiac Progenitor Cells and the Interplay with Their Microenvironment

The microenvironment plays a crucial role in the behavior of stem and progenitor cells. In the heart, cardiac progenitor cells (CPCs) reside in specific niches, characterized by key components that are altered in response to a myocardial infarction. To date, there is a lack of knowledge on these niches and on the CPC interplay with the niche components. Insight into these complex interactions and into the influence of microenvironmental factors on CPCs can be used to promote the regenerative potential of these cells. In this review, we discuss cardiac resident progenitor cells and their regenerative potential and provide an overview of the interactions of CPCs with the key elements of their niche. We focus on the interaction between CPCs and supporting cells, extracellular matrix, mechanical stimuli, and soluble factors. Finally, we describe novel approaches to modulate the CPC niche that can represent the next step in recreating an optimal CPC microenvironment and thereby improve their regeneration capacity.

Induced pluripotent stem cell modelling of HLHS underlines the contribution of dysfunctional NOTCH signalling to impaired cardiogenesis

Hypoplastic left heart syndrome (HLHS) is among the most severe forms of congenital heart disease. Although the consensus view is that reduced flow through the left heart during development is a key factor in the development of the condition, the molecular mechanisms leading to hypoplasia of left heart structures are unknown. We have generated induced pluripotent stem cells (iPSC) from five HLHS patients and two unaffected controls, differentiated these to cardiomyocytes and identified reproducible in vitro cellular and functional correlates of the HLHS phenotype. Our data indicate that HLHS-iPSC have a reduced ability to give rise to mesodermal, cardiac progenitors and mature cardiomyocytes and an enhanced ability to differentiate to smooth muscle cells. HLHS-iPSC-derived cardiomyocytes are characterised by a lower beating rate, disorganised sarcomeres and sarcoplasmic reticulum and a blunted response to isoprenaline. Whole exome sequencing of HLHS fibroblasts identified deleterious variants in NOTCH receptors and other genes involved in the NOTCH signalling pathway. Our data indicate that the expression of NOTCH receptors was significantly downregulated in HLHS-iPSC-derived cardiomyocytes alongside NOTCH target genes confirming downregulation of NOTCH signalling activity. Activation of NOTCH signalling via addition of Jagged peptide ligand during the differentiation of HLHS-iPSC restored their cardiomyocyte differentiation capacity and beating rate and suppressed the smooth muscle cell formation. Together, our data provide firm evidence for involvement of NOTCH signalling in HLHS pathogenesis, reveal novel genetic insights important for HLHS pathology and shed new insights into the role of this pathway during human cardiac development.

Notch Signaling in Ischemic Damage and Fibrosis: Evidence and Clues from the Heart

Notch signaling is a major intercellular coordination mechanism highly conserved throughout evolution. In vertebrates, Notch signaling is physiologically involved in embryo development, including mesenchymal cell commitment, formation of heart tissues and angiogenesis. In post-natal life, Notch signaling is maintained as a key mechanism of cell–cell communication and its dysregulations have been found in pathological conditions such as ischemic and fibrotic diseases. In the heart, Notch takes part in the protective response to ischemia, being involved in pre- and post-conditioning, reduction of reperfusion-induced oxidative stress and myocardial damage, and cardiomyogenesis. Conceivably, the cardioprotective effects of Notch may depend on neo-angiogenesis, thus blunting lethal myocardial ischemia, as well as on direct stimulation of cardiac cells to increase their resistance to injury. Another post-developmental adaptation of Notch signaling is fibrosis: being involved in the orientation of mesenchymal cell fate, Notch can modulate the differentiation of pro-fibrotic myofibroblasts, e.g., by reducing the effects of the profibrotic cytokine TGF-β. In conclusion, Notch can regulate the interactions between heart muscle and stromal cells and switch cardiac repair from a pro-fibrotic default pathway to a pro-cardiogenic one. These features make Notch signaling a suitable target for new cardiotropic therapies.

Implantation of a Poly-L-Lactide GCSF-Functionalized Scaffold in a Model of Chronic Myocardial Infarction

A previously developed poly-l-lactide scaffold releasing granulocyte colony-stimulating factor (PLLA/GCSF) was tested in a rabbit chronic model of myocardial infarction (MI) as a ventricular patch. Control groups were constituted by healthy, chronic MI and nonfunctionalized PLLA scaffold. PLLA-based electrospun scaffold efficiently integrated into a chronic infarcted myocardium. Functionalization of the biopolymer with GCSF led to increased fibroblast-like vimentin-positive cellular colonization and reduced inflammatory cell infiltration within the micrometric fiber mesh in comparison to nonfunctionalized scaffold; PLLA/GCSF polymer induced an angiogenetic process with a statistically significant increase in the number of neovessels compared to the nonfunctionalized scaffold; PLLA/GCSF implanted at the infarcted zone induced a reorganization of the ECM architecture leading to connective tissue deposition and scar remodeling. These findings were coupled with a reduction in end-systolic and end-diastolic volumes, indicating a preventive effect of the scaffold on ventricular dilation, and an improvement in cardiac performance.

Cardiomyocyte Lineage Specification in Adult Human Cardiac Precursor Cells Via Modulation of Enhancer-Associated Long Noncoding RNA Expression

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Human CPCs produce predominantly smooth muscle cells.

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CPCs can be redirected to the cardiomyocyte fate by transient activation followed by inhibition of NOTCH signaling.

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Inhibition of NOTCH signaling during differentiation represses MIR-143/145 expression and blocks smooth muscle differentiation.

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Expression of the microRNAs is under control of CARMEN, a long noncoding RNA associated with an enhancer located in the MIR-143/145 locus and target of NOTCH signaling.

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The CARMEN/MIR-145/143 locus represents a promising therapeutic target to favor production of cardiomyocytes in cell replacement therapies.

The mechanisms controlling differentiation in adult cardiac precursor cells (CPCs) are still largely unknown. In this study, CPCs isolated from the human heart were found to produce predominantly smooth muscle cells but could be redirected to the cardiomyocyte fate by transient activation followed by inhibition of NOTCH signaling. NOTCH inhibition repressed MIR-143/145 expression, and blocked smooth muscle differentiation. Expression of the microRNAs is under control of CARMEN, a long noncoding RNA associated with an enhancer located in the MIR-143/145 locus and target of NOTCH signaling. The CARMEN/MIR-145/143 axis represents, therefore, a promising target to favor production of cardiomyocytes in cell replacement therapies.

Notch signalling suppresses regulatory T-cell function in murine experimental autoimmune uveitis

Autoimmune uveitis is an intraocular inflammatory disorder in developed countries. Understanding the mechanisms underlying the development and modulation of immune reaction in uveitic eyes is critical for designing therapeutic interventions. Here we investigated the role of Notch signalling in regulatory T-cell (Treg cell) function during experimental autoimmune uveitis (EAU). Using the Foxp3-GFP reporter mouse strain, the significance of Notch signalling for the function of infiltrating Treg cells was characterized in an EAU model. We found that infiltrating Treg cells substantially expressed Notch-1, Notch-2, JAG1 and DLL1 in uveitic eyes. Activation of Notch signalling, represented by expression of HES1 and HES5, was enhanced in infiltrating Treg cells. Treatment with JAG1 and DLL1 down-regulated Foxp3 expression and immunosuppressive activity of isolated infiltrating Treg cells in vitro, whereas neutralizing antibodies against JAG1 and DLL1 diminished Notch ligand-mediated negative effects on Treg cells. To investigate the significance of Notch signalling for Treg cell function in vivo, lentivirus-derived Notch short hairpin RNAs were transduced into in vitro expanded Treg cells before adoptive transfer of Treg cells into EAU mice. Transfer of Notch-1-deficient Treg cells remarkably reduced pro-inflammatory cytokine production and inflammatory cell infiltration in uveitic eyes. Taken together, Notch signalling negatively modulates the immunosuppressive function of infiltrating Treg cells in mouse EAU.

NOTCH1 mediates a switch between two distinct secretomes during senescence

Senescence, a persistent form of cell-cycle arrest, is often associated with a diverse secretome, which provides complex functionality for senescent cells within the tissue microenvironment. We show that oncogene-induced senescence is accompanied by a dynamic fluctuation of NOTCH1 activity, which drives a TGF-β-rich secretome, while suppressing the senescence-associated pro-inflammatory secretome through inhibition of C/EBPβ. NOTCH1 and NOTCH1-driven TGF-β contribute to 'lateral induction of senescence' through a juxtacrine NOTCH-JAG1 pathway. In addition, NOTCH1 inhibition during senescence facilitates upregulation of pro-inflammatory cytokines, promoting lymphocyte recruitment and senescence surveillance in vivo. As enforced activation of NOTCH1 signalling confers a near mutually exclusive secretory profile compared with typical senescence, our data collectively indicate that the dynamic alteration of NOTCH1 activity during senescence dictates a functional balance between these two distinct secretomes: one representing TGF-β and the other pro-inflammatory cytokines, highlighting that NOTCH1 is a temporospatial controller of secretome composition.

Cardiomyocytes in Young Infants With Congenital Heart Disease: a Three-Month Window of Proliferation

Perinatal reduction in cardiomyocyte cell cycle activity is well established in animal models and humans. However, cardiomyocyte cell cycle activity in infants with congenital heart disease (CHD) is unknown, and may provide important information to improve treatment. Human right atrial specimens were obtained from infants during routine surgery to repair ventricular septal defects. The specimens were divided into three groups: group A (age 1–3 months); group B (age, 4–6 months); and group C (age 7–12 months). A dramatic fall in the number of Ki67 -positive CHD cardiac myocytes occurred after three months. When cultured in vitro, young CHD myocytes (≤3 months) showed more abundant Ki67-positive cardiomyocytes and greater incorporation of EdU, indicating enhanced proliferation. YAP1 and NICD—important transcript factors in cardiomyocyte development and proliferation—decreased with age and β-catenin increased with age. Compared with those of older infants, cardiomyocytes of young CHD infants (≤3 months) have a higher proliferating capacity in vivo and in vitro. From the perspective of cardiac muscle regeneration, CHD treatment at a younger age (≤3 months) may be more optimal.

A Novel Class of Human Cardiac Stem Cells

Following the recognition that hematopoietic stem cells improve the outcome of myocardial infarction in animal models, bone marrow mononuclear cells, CD34-positive cells, and mesenchymal stromal cells have been introduced clinically. The intracoronary or intramyocardial injection of these cell classes has been shown to be safe and to produce a modest but significant enhancement in systolic function. However, the identification of resident cardiac stem cells in the human heart (hCSCs) has created great expectation concerning the potential implementation of this category of autologous cells for the management of the human disease. Although phase 1 clinical trials have been conducted with encouraging results, the search for the most powerful hCSC for myocardial regeneration is in its infancy. This manuscript discusses the efforts performed in our laboratory to characterize the critical biological variables that define the growth reserve of hCSCs. Based on the theory of the immortal DNA template, we propose that stem cells retaining the old DNA represent 1 of the most powerful cells for myocardial regeneration. Similarly, the expression of insulin-like growth factor-1 receptors in hCSCs recognizes a cell phenotype with superior replicating reserve. However, the impressive recovery in ventricular hemodynamics and anatomy mediated by clonal hCSCs carrying the "mother" DNA underscores the clinical relevance of this hCSC class for the treatment of human heart failure.

Cellular and molecular mechanisms of HGF/Met in the cardiovascular system

Met tyrosine kinase receptor, also known as c-Met, is the HGF (hepatocyte growth factor) receptor. The HGF/Met pathway has a prominent role in cardiovascular remodelling after tissue injury. The present review provides a synopsis of the cellular and molecular mechanisms underlying the effects of HGF/Met in the heart and blood vessels. In vivo, HGF/Met function is particularly important for the protection of the heart in response to both acute and chronic insults, including ischaemic injury and doxorubicin-induced cardiotoxicity. Accordingly, conditional deletion of Met in cardiomyocytes results in impaired organ defence against oxidative stress. After ischaemic injury, activation of Met provides strong anti-apoptotic stimuli for cardiomyocytes through PI3K (phosphoinositide 3-kinase)/Akt and MAPK (mitogen-activated protein kinase) cascades. Recently, we found that HGF/Met is also important for autophagy regulation in cardiomyocytes via the mTOR (mammalian target of rapamycin) pathway. HGF/Met induces proliferation and migration of endothelial cells through Rac1 (Ras-related C3 botulinum toxin substrate 1) activation. In fibroblasts, HGF/Met antagonizes the actions of TGFβ1 (transforming growth factor β1) and AngII (angiotensin II), thus preventing fibrosis. Moreover, HGF/Met influences the inflammatory response of macrophages and the immune response of dendritic cells, indicating its protective function against atherosclerotic and autoimmune diseases. The HGF/Met axis also plays an important role in regulating self-renewal and myocardial regeneration through the enhancement of cardiac progenitor cells. HGF/Met has beneficial effects against myocardial infarction and endothelial dysfunction: the cellular and molecular mechanisms underlying repair function in the heart and blood vessels are common and include pro-angiogenic, anti-inflammatory and anti-fibrotic actions. Thus administration of HGF or HGF mimetics may represent a promising therapeutic agent for the treatment of both coronary and peripheral artery disease.

Biomimetic approaches for cell implantation to the restoration of infarcted myocardium

Compelling evidences accumulated over the years have proven stem cells as a promising source for regenerative medicine. However, the inadequacy with the design of delivery modalities has prolonged the research in realizing an ideal cell-based approach for the regeneration of infarcted myocardium. Currently, some modest improvements in cardiac function have been documented in clinical trials with stem cell treatments, although regenerating a fully functional myocardium remains a dream for cardiac surgeons. This review provides an overview on the significance of stem cell therapy, the current attempts to resolve the drawbacks with the cell implantation approach and the various stratagems adopted with electrospun hybrid nanofibers for implementation in myocardial regenerative therapy.

Notch signaling represses GATA4-induced expression of genes involved in steroid biosynthesis

Notch2 and Notch3 and genes of the Notch signaling network are dynamically expressed in developing follicles, where they are essential for granulosa cell proliferation and meiotic maturation. Notch receptors, ligands, and downstream effector genes are also expressed in testicular Leydig cells, predicting a potential role in regulating steroidogenesis. In this study, we sought to determine if Notch signaling in small follicles regulates the proliferation response of granulosa cells to FSH and represses the up-regulation steroidogenic gene expression that occurs in response to FSH as the follicle grows. Inhibition of Notch signaling in small preantral follicles led to the up-regulation of the expression of genes in the steroid biosynthetic pathway. Similarly, progesterone secretion by MA-10 Leydig cells was significantly inhibited by constitutively active Notch. Together, these data indicated that Notch signaling inhibits steroidogenesis. GATA4 has been shown to be a positive regulator of steroidogenic genes, including STAR protein, P450 aromatase, and 3B-hydroxysteroid dehydrogenase. We observed that Notch downstream effectors HEY1, HEY2, and HEYL are able to differentially regulate these GATA4-dependent promoters. These data are supported by the presence of HEY/HES binding sites in these promoters. These studies indicate that Notch signaling has a role in the complex regulation of the steroidogenic pathway.

Intramyocardial Delivery of Notch Ligand-Containing Hydrogels Improves Cardiac Function and Angiogenesis Following Infarction

Myocardial infarction (MI) is the leading cause of death worldwide. Notch1 signaling plays a critical role in cardiac development, in survival, cardiogenic lineage commitment, differentiation of cardiac stem/progenitor cells, and in regenerative responses following myocardial injury. The objective of this study was the evaluation of the therapeutic effect of delivering the Notch ligand-containing hydrogels in a rat model of MI. Self-assembling peptide (SAP) hydrogels were functionalized with a peptide mimic of the Notch1 ligand Jagged1 (RJ). In rats subjected to experimental MI, delivery of RJ-containing hydrogel to the infarcted heart resulted in improvement in cardiac function back to sham-operated levels. A significant decrease in fibrosis and an increase in the endothelial vessel area and Ki67 expression were also observed in rats treated with the RJ hydrogels compared to untreated rats or rats treated with unmodified or scrambled peptide hydrogels. This study demonstrates the functional benefit of Notch1-activating peptide delivered in SAP hydrogels for cardiac repair.

Activation of Notch1 signalling promotes multi-lineage differentiation of c-Kit(POS)/NKX2.5(POS) bone marrow stem cells: implication in stem cell translational medicine

Introduction

Transplantation of bone marrow mesenchymal stem cells (BMSCs) can repair injured hearts. However, whether BMSC populations contain cells with cardiac stem cell characteristics is ill-defined. We report here that Notch signalling can promote differentiation of c-Kit^POS/NKX2.5^POS BMSCs into cardiomyocyte-like cells.

Methods

Total BMSCs were isolated from Sprague–Dawley rat femurs and c-Kit^POS cells were purified. c-Kit^POS/NKX2.5^POS cells were isolated by single-cell cloning, and the presence of cardiomyocyte, smooth muscle cell (SMC), and endothelial cell differentiation markers assessed by immunofluorescence staining and semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis. Levels of c-Kit and Notch1–4 in total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs were quantitated by flow cytometry. Following infection with an adenovirus over-expressing Notch1 intracellular domain (NICD), total BMSCs and c-Kit^POS/NKX2.5^POS cells were assessed for differentiation to cardiomyocyte, SMC, and endothelial cell lineages by immunofluorescence staining and real-time quantitative RT-PCR. Total BMSCs and c-Kit^POS/NKX2.5^POS cells were treated with the Notch1 ligand Jagged1 and markers of cardiomyocyte, SMC, and endothelial cell differentiation were examined by immunofluorescence staining and real-time quantitative RT-PCR analysis.

Results

c-Kit^POS/NKX2.5^POS cells were present among total BMSC populations, and these cells did not express markers of adult cardiomyocyte, SMC, or endothelial cell lineages. c-Kit^POS/NKX2.5^POS BMSCs exhibited a multi-lineage differentiation potential similar to total BMSCs. Following sorting, the c-Kit level in c-Kit^POS/NKX2.5^POS BMSCs was 84.4%. Flow cytometry revealed that Notch1 was the predominant Notch receptor present in total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs. Total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs overexpressing NICD had active Notch1 signalling accompanied by differentiation into cardiomyocyte, SMC, and endothelial cell lineages. Treatment of total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs with exogenous Jagged1 activated Notch1 signalling and drove multi-lineage differentiation, with a tendency towards cardiac lineage differentiation in c-Kit^POS/NKX2.5^POS BMSCs.

Conclusions

c-Kit^POS/NKX2.5^POS cells exist in total BMSC pools. Activation of Notch1 signalling contributed to multi-lineage differentiation of c-Kit^POS/NKX2.5^POS BMSCs, favouring differentiation into cardiomyocytes. These findings suggest that modulation of Notch1 signalling may have potential utility in stem cell translational medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0085-2) contains supplementary material, which is available to authorized users.

c-kit(+) cells: the tell-tale heart of cardiac regeneration?

Cardiovascular disease is the leading cause of morbidity and mortality in the developed world. Although ongoing therapeutic strategies ameliorate symptoms and prolong life for patients with cardiovascular diseases, they do not solve the critical issue related to the loss of cardiac tissue. Accordingly, stem/progenitor cell therapy has emerged as a paramount approach for cardiac repair and regeneration. In this regard, c-kit(+) cells have animated much interest and controversy. These cells are self-renewing, clonogenic, and multipotent and display a noteworthy potential to differentiate into all cardiovascular lineages. However, their functional contribution to cardiomyocyte turnover is one of the centrally debated issues concerning their regenerative potential. Regardless, plentiful preclinical and clinical studies have been conducted which provide evidence for the capacity of c-kit(+) cells to improve cardiac function. The purpose of this review is to give a comprehensive, impartial, critical description and evaluation of the literature on c-kit(+) cells from bench to bedside in order to address their true potential, benefits and controversies.

Notch activation enhances lineage commitment and protective signaling in cardiac progenitor cells

Phase I clinical trials applying autologous progenitor cells to treat heart failure have yielded promising results; however, improvement in function is modest, indicating a need to enhance cardiac stem cell reparative capacity. Notch signaling plays a crucial role in cardiac development, guiding cell fate decisions that underlie myocyte and vessel differentiation. The Notch pathway is retained in the adult cardiac stem cell niche, where level and duration of Notch signal influence proliferation and differentiation of cardiac progenitors. In this study, Notch signaling promotes growth, survival and differentiation of cardiac progenitor cells into smooth muscle lineages in vitro. Cardiac progenitor cells expressing tamoxifen-regulated intracellular Notch1 (CPCeK) are significantly larger and proliferate more slowly than control cells, exhibit elevated mTORC1 and Akt signaling, and are resistant to oxidative stress. Vascular smooth muscle and cardiomyocyte markers increase in CPCeK and are augmented further upon ligand-mediated induction of Notch signal. Paracrine signals indicative of growth, survival and differentiation increase with Notch activity, while markers of senescence are decreased. Adoptive transfer of CPCeK into infarcted mouse myocardium enhances preservation of cardiac function and reduces infarct size relative to hearts receiving control cells. Greater capillary density and proportion of vascular smooth muscle tissue in CPCeK-treated hearts indicate improved vascularization. Finally, we report a previously undescribed signaling mechanism whereby Notch activation stimulates CPC growth, survival and differentiation via mTORC1 and paracrine factor expression. Taken together, these findings suggest that regulated Notch activation potentiates the reparative capacity of CPCs in the treatment of cardiac disease.